1. Field of the Invention
This invention generally relates to an energy efficient transparent structure and, more particularly, to a solar film layer(s) capable of selectively transmitting light based upon the criteria of wavelength or angle of incidence, while selectively reflecting light for the purpose of generating energy.
2. Description of the Related Art
The windows of commercial and residential buildings represent a substantial opportunity for energy generation, but window transparency is critical. Therefore, an approach is needed to capture solar radiation at low cost, without compromising the window's transparency. Due to the large surface area of building windows, windows can be used to capture solar energy. This idea is attractive if transparency is maintained and the additional cost is low. As part of the new opportunity presented from building integrated photovoltaics (BIPV), building windows can be used to generate clean alternative energy.
The emerging market for BIPV offers a new opportunity to develop revenue streams for both building and solar industries that have been under stress in recent years. The advantage of integrated photovoltaics over conventional non-integrated systems is that the initial cost can be offset by reducing what is spent on building materials and labor that would normally be used to construct the part of the building being replaced by the BIPV modules, such as roof, skylights, facades, or windows. According to a recent market report, the global market for BIPV is expected to reach the capacity of 11,392 megawatts by the year 2015 at the compounded annual growth rate of 56%. The growing demand for energy-efficient, flexible, and transparent solar materials is transforming the way architects and manufacturers use photovoltaic systems.
Concurrent with the BIPV opportunity is smart window technology that may possibly replace existing building windows. According to the U.S. Dept. of Energy, homes and commercial buildings consume approximately 40% of the electricity used in the United States, costing consumers approximately US$200 billion annually. One solution to reducing the energy consumption of personal and commercial buildings is smart window technology, which reduces the amount of solar heat entering the building by altering the transparency of the windows to reject part of visible and near-infrared (NIR) light. The investment in smart window installation is offset by the energy savings realized from reducing the cost of heating, ventilation, air conditioning (HVAC) systems. However, currently all of the smart window technologies require an electrical power source to activate the tinting features of the windows. By applying source voltages, the light transmittance, transparency, or shading of windows can dynamically change. This feature adds a significant amount to the installation cost of smart windows, as electrical wires need to be connected from all the windows to a main controller.
It would be advantageous if a smart window could be self-powered with solar energy and controlled without any electrical wiring, reducing the overall labor cost and installed system price of the smart window.